Organically-modified silicates are organic-inorganic hybrid materials in which the organic moieties are covalently linked to the siloxane backbone (L. Nicole, L. Rozes, C. Sanchez, Adv. Mater., 2010, 22, 3208). Their rheological behavior may be modified by varying the precursor ratios, resulting in materials exhibiting rubbery or brittle characteristics (J. D. Mackenzie, Y. J. Chung, Y. Hu, J. Non-Cryst. Solids, 1992, 147-148, 271). Silsesquioxanes ([RSiO1.5]n) are specific examples of organically-modified silicates in which R is hydrogen or any organic group (e.g., alkyl, alkylene, aryl, etc.). Silsesquioxanes or silsesquioxane-silica hybrids are synthesized using a Stöber-like sol-gel route (W. Stöber, A. Fink, E. Bohn, J. Colloid Interface Sci., 1968, 26, 62), via hydrolytic condensation of trialkoxysilanes, bridged alkoxides or co-condensation between a tetra-alkoxysilane and a trialkoxysilane (F. Hoffmann, M. Cornelius, J. Morell, M. Fröba, Angew. Chem. Int. Ed., 2006, 45, 3216; H. Mori, Y. Miyamura, T. Endo, Langmuir, 2007, 23, 9014; E. Ruiz-Hitzky, P. Aranda, M. Darder, M. Ogawa, Chem. Soc. Rev., 2011, 40, 801). By controlling the organic-inorganic composition, as well as functionality of these hybrid materials, a wide variety of silicate-based hybrid materials may be produced for applications in the fields of catalysis (F. Hoffmann, M. Cornelius, J. Morell, M. Fröba, Angew. Chem. Int. Ed., 2006, 45, 3216), optical devices (C. Sanchez, B. Lebeau, F. Chaput, J. P. Boilot, Adv. Mater., 2003, 15, 1969), coating and polymer science (X. X. Zhang, B. B. Xia, H. P. Ye, Y. L. Zhang, B. Zhao, L. H. Yan, H. B. Lv, B. Jiang, J. Mater. Chem., 2012, 22, 13132; B. M. Novak, Adv. Mater., 1993, 5, 422).
The introduction of reactive functionalities to silsesquioxanes may be achieved via post-synthetic surface functionalization procedures (grafting), which are based upon chemical reaction of silica particles with coupling agents bearing organic functional groups. However, the limitations of the grafting method are that there are relatively few silanol groups available on the surface of the silica particles and the procedure is time-consuming. In addition, this method generally results in particles containing only one type of functional group.
Recently, efforts have been made to explore the ability of organosilanes with surfactant chain-bearing groups to self-direct the hydrolysis and condensation of alkoxysilane precursors into structures with mesoporous characteristics (G. Büchel, K. Klaus, K. K. Unger, A. Matsumoto, K. Tsutsumi, Adv. Mater., 1998, 10, 1036; E. Ruiz-Hitzky, S. Letaïef, V. Prévot, Adv. Mater., 2002, 14, 439; Y. Fujimoto, A. Shimojima, K. Kuroda, J. Mater. Chem., 2006, 16, 986; M. Choi, H. S. Cho, R. Sricastava, C. Venkatesan, D. H. Choi, R. Ryoo, Nat. Mater., 2006, 5, 718). Although the mechanisms of using surfactant silanes to facilitate formation of particles with tailored mesostructures (i.e., mesoporous, lamellar, and worm-like mesostrucutures) were well understood, little is known regarding the synthesis of mesostructured hybrid materials with dual functionalities.
Accordingly, there is a need for methods of preparing silsesquioxane-silica hybrids and for preparing particles containing these hybrids having mesoporous characteristics. The methods and compositions of the present invention are directed toward these, as well as other, important ends.